1. Field of the Invention
The present invention relates to a protractor and ruler combination and, more particularly, to a protractor and ruler combination, wherein the included angle between the ruler section of the main ruler and the ruler section of the auxiliary ruler is measured exactly.
2. Description of the Related Art
A conventional protractor and ruler combination 10 in accordance with the prior art shown in FIGS. 7–9 comprises a ruler 20 having a first side formed with a plurality of scales 201 and a second side 202 formed with a contrast portion 203 having a reading scale 204, a protractor 30 rotatably mounted on the ruler 20 and having a plurality of scales 301, a threaded rod 302 mounted on the protractor 30 and extended through the ruler 20, a washer 303 mounted on the threaded rod 302, and a nut 304 screwed on the threaded rod 302. In practice, the ruler 20 is rotated relative to the protractor 30 as shown in FIG. 9, so that the user can identify the included angle between the ruler 20 and the protractor 30 by matching the reading scale 204 of the contrast portion 203 with one of the scales 301 of the protractor 30.
However, the user cannot identify the included angle between the ruler 20 and the protractor 30 exactly. In addition, the ruler 20 rubs the protractor 30 frequently, so that the scales 301 of the protractor 30 are easily worn out due to frequent friction and contact, thereby causing inconvenience to the user in identification and measurement of the included angle between the ruler 20 and the protractor 30.